The present invention relates to an optical transmitter-receiver module and an electronic device for use in a single-core bidirectional optical transmitter-receiver system capable of performing transmission and reception with a single-core optical fiber. The present invention relates, in particular, to a digital communication system, which is able to perform high-speed transmission, such as IEEE1394 (Institute of Electrical and Electronic Engineers 1394) and USB (Universal Serial Bus) 2.0.
Conventionally, as an optical transmitter-receiver module, there is a one as described in Japanese Patent Laid-Open Publication No. 2001-147349. As shown in FIG. 35, this optical transmitter-receiver module has an optical system using a prism 1104 and achieves full-duplex communications with a single-core optical fiber cable by employing a light-tight partition plate 1111 that abuts against an end surface of an optical fiber 1102 so as to separate a light-emitting device and a light-receiving device from each other to thereby reduce optical crosstalk.
As shown in FIG. 35, in this optical transmitter-receiver module, the partition plate 1111 abuts against the end surface of the optical fiber 1102 in an optical plug 1101, and a light-emitting element 1103 and a light-receiving element 1105 are molded or encapsulated with a molding resin 1106. Lens portions 1106a and 1106b are integrally formed in the plastic molding stage of the molding resin.
In the above-mentioned optical transmitter-receiver module, the light-emitting element 1103 and the light-receiving element 1105 are arranged in positions (on a substrate 1109) located at same distance in the direction of the optical axis from the tip of the optical fiber 1102. Moreover, the prism 1104 is arranged such that halves thereof on the transmission side and the reception side are located at same distance in the direction of the optical axis from the tip of the optical fiber 1102. The partition plate 1111 is elastically deformed by abutting against the optical fiber 1102, providing a structure in which no gap exists between the end surface of the optical fiber 1102 and a surface facing the optical fiber 1102 of the partition plate 1111.
The above-mentioned optical transmitter-receiver module employs a prism optical system having the partition plate 1111 and has the structure in which the end surface of the optical fiber 1102 abuts against the partition plate 1111. Accordingly, there is a problem that the end surface of the optical fiber 1102 and/or the partition plate 1111 is damaged. Moreover, with the partition plate 1111 provided, transmission light is emitted by about 50% with regard to the projected area of the optical fiber, and reception light is made incident by about 50% with regard to the projected area of the optical fiber. Since the light-emitting element 1103 and the light-receiving element 1105 are located at the same distance in the direction of the optical axis from the end surface of the optical fiber 1102, it is difficult to increase the transmission efficiency and reception efficiency. Furthermore, due to a restriction attributed to the structure of the partition plate 1111, the optical layout of the optical elements is not very appropriate to obtain a good performance of optical coupling of the single-core optical fiber cable with the light-emitting element 1103 and/or the light-receiving element 1105.
Accordingly, an object of this invention is to provide an optical transmitter-receiver module and an electronic device using the same, which module is able to perform high-quality optical transmission by full-duplex communication scheme by using a light-tight partition plate and able to prevent the optical fiber end surface and the partition plate from being damaged even if the inserted optical plug is rotated in the module, and which module has an optical layout good enough to obtain a satisfactory performance of optical coupling of the single-core optical fiber cable with the light-emitting element and the light-receiving element.
In order to accomplish the above object, the present invention provides an optical transmitter-receiver module having a light-emitting element for emitting transmission signal light and a light-receiving element for receiving reception signal light, said module being able to perform both transmission of the transmission signal light and reception of the reception signal light by means of a single-core optical fiber, said module comprising:
a jack section for detachably holding an optical plug provided at an end portion of the optical fiber;
a light emitting/receiving unit having the light-emitting element and light-receiving element positioned and fixed in place and molded in one piece; and
a light-tight partition plate unit for separating an optical path of the transmission signal light and an optical path of the reception signal light from each other, said light-tight partition plate being arranged so as to be held between the jack section and the light emitting/receiving unit,
the light-emitting element being located at a larger distance in a direction of optical axis of the optical fiber from an end surface of the optical fiber than the light-receiving element is.
According to the optical transmitter-receiver module of the above construction, by arranging the light-tight partition plate unit for separation between the optical path of the transmission signal light and the optical path of the reception signal light so that the plate is held between the jack section and the light emitting/receiving unit, the coupling of the transmission signal light directly with the light-receiving element is restrained, so that high-quality optical transmission by the full-duplex communication method is achieved. Furthermore, by arranging the light-emitting element so that it is located at a greater distance in the direction of the optical axis from the optical fiber end surface than the light-receiving element is, an optical layout realizing a satisfactory optical coupling of the single-core optical fiber cable with the light-emitting element and the light-receiving element can be provided.
In one embodiment, the module has a transmission prism for refracting the transmission signal light emitted from the light-emitting element and guiding the light to the optical fiber end surface, and a reception prism for refracting at least part of the reception signal light emitted from the optical fiber and guiding the part of light to the light-receiving element. The transmission prism is arranged at a greater distance in the direction of the optical axis from the optical fiber end surface than the reception prism is.
According to the optical transmitter-receiver module of the above-mentioned embodiment, by keeping the light-emitting element away from the optical fiber end surface with the transmission prism located at a greater distance in the direction of the optical axis from the optical fiber end surface than the reception prism is, it is possible to reduce an angle made between a direction of emission of the light-emitting element and the optical axis of the optical fiber. The smaller the angle is, the further the transmission efficiency is improved because the transmission light can be coupled with the optical fiber without being excessively bent by the transmission prism. On the other hand, with the reception prism located in a position closer to the end surface of the optical fiber, the reception signal light from the optical fiber end surface is bent toward the reception side by the reception prism for the coupling with the reception element before the light spreads, whereby the reception efficiency is improved.
In one embodiment, the light emitting/receiving unit has not only the light-emitting element and light-receiving element but also the transmission prism and reception prism positioned and fixed in place and molded in one piece.
This arrangement enables the optimization of the optical layout and the downsizing of the optical transmitter-receiver module proper.
In one embodiment, the optical transmitter-receiver module further has a positioning means for positioning the transmission prism and the reception prism, said positioning means having projections provided at either the transmission and reception prisms or the light-receiving/emitting unit, and associated holes provided at the light-receiving/emitting unit or the transmission and reception prisms that has/have said projections, and positioning the transmission prism and the reception prism by inserting the projections into the respective associated holes.
According to this embodiment, because the positioning of the transmission prism and the reception prism is achieved only by inserting the projections into the respective holes, the positioning accuracy of these prisms can easily be improved.
In one embodiment, at least one projection or hole for the transmission prism is provided in a region through which the transmission signal light does not pass. Also, at least one projection or hole for the reception prism is provided in a region through which the reception signal light does not pass.
With this arrangement, the positioning means can be provided without affecting the transmission and reception performance.
In one embodiment, the transmission prism and the reception prism positioned by the positioning means are fixed by resin molding to a resin-molded piece to which the light-emitting element and the light-receiving element are positioned and fixed.
This arrangement easily prevents the transmission prism and the reception prism from being detached.
In one embodiment, a partition plate included in the partition plate unit is placed in a partition plate guiding groove provided between a transmission side and a reception side of the light-receiving/emitting unit. Also, the partition plate is sized such that a distance in the direction of optical axis of the optical fiber from said end surface of the optical fiber to an end opposite from the optical fiber of the partition plate is greater than a distance in the direction of optical axis from said end surface of the optical fiber to a bottom of a transmission lens provided on emission side of the light-emitting element.
With this arrangement, the transmission signal light (including reflection light) emitted from the light-emitting element can reliably be prevented from being incident on the light-receiving element, whereby the optical crosstalk can effectively be reduced.
By employing the above-mentioned optical transmitter-receiver module, there can be provided electronic equipment such as an information domestic appliance capable of performing optical transmission by a high-quality full-duplex communication system.